The trend of making AV equipment or electronic equipment such as PCs and mobile communication devices more compact and cordless is accelerated in recent years. For the driving power sources for these electric equipment, nickel cadmium storage batteries, nickel metal-hydride storage batteries, and lithium ion secondary batteries are used because of their high reliability and easy maintenance.
Hybrid electric vehicles, on the other hand, use nickel metal-hydride storage batteries as the power source of the battery-driven motor that is used as the vehicle's driving power source in combination with an internal-combustion engine. For emergency backup power during power outages due to natural disasters such as earthquakes or typhoons, lead storage batteries are most commonly used at the present day, but future practical application of nickel metal-hydride storage batteries is desired, as they have a large capacity and are capable of discharging at a large current. Other expected applications of the large-capacity nickel metal-hydride storage battery include emergency power in unmanned communication bases, and railway power applications such as power source for lifting up train's pantographs, or lighting backup power to be used when power supply to the train is stopped.
The power source device used in the above applications is generally constructed as a battery pack; a necessary number of battery modules are interconnected to provide a desired output voltage, each battery module consisting of a plurality of cylindrical batteries with their power terminals of opposite polarities being connected to each other. A prior application by the applicants of the present invention shows a battery module having high rigidity to withstand vibration or impact (see, for example, Patent Document 1).
The above battery module includes a plastic rectangular parallelepiped holder case having a thickness generally equal to the axial length of the cylindrical batteries. Battery compartment, which is square in top view with its one side being generally equal to the diameter of the cylindrical battery, is formed in one or a plurality of rows extending through the thickness of the case. Opposite polarity terminals of each two adjacent cylindrical batteries which are individually accommodated in these battery compartments are electrically interconnected using flat connection plates. The inter-battery connection structure for connecting each two adjacent cylindrical batteries includes a ring-shaped connection electrode axially protruding outwards from near the outer periphery of the cylindrical battery, the flat connection plate being bridged across the connection electrode of one of each two adjacent cylindrical batteries and the bottom face of the other battery. The contact points between the connection plate and connection electrode and between the connection plate and the bottom face of the battery case are bonded together by welding.
Since the cylindrical batteries are respectively accommodated in their compartments and completely electrically isolated from each other, the battery module requires no insulation rings or outer tubes, whereby a cost reduction is achieved and productivity is improved. Also, since the cylindrical batteries make contact with four partition walls that form the battery compartment at four circumferential points and are thereby fixed in position, they are tightly held even when vibration or impact is applied, and thus the battery module provides a remarkable effect of firm retention of the batteries.
Another known conventional battery pack uses a plastic box-like rectangular holder case with an open top for holding several rows of battery modules in multiple tiers inserted therein; each battery module consists of a plurality of cylindrical batteries electrically connected in series and mechanically coupled together in a row. End plates at both ends of the holder case include bus bars for electrically interconnecting the terminals of the battery modules (see, for example, Patent Document 2). The holder case includes circular through holes in both end walls in the same number as the number of battery modules to be accommodated, which are generally long and columnar in outer shape. Intermediate walls for ensuring stable hold of battery modules are arranged in parallel to both end walls, and are formed with the same number of circular through holes as that of the end walls. The battery modules are inserted into the through holes of the end walls and intermediate walls and thereby held in position in the holder case.
This battery pack has much higher support strength for the battery modules and higher rigidity, and since the battery modules can be coupled to bus bars only by fastening bolts or the like, the process of mounting the battery modules into the holder case is simple and easy.
[Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-162993
[Patent Document 2] Japanese Patent Laid-Open Publication No. 10-270006